Annular fissures, also known as annular tears, are a degenerative deficiency of one or more layers that make up the annulus fibrosus of the intervertebral disc. 

Terminology

Many authors prefer the term "annular fissure" over "annular tear", as the latter seems to imply acute injury ^1,2. In the setting of severe trauma with disruption of the disc, the term "disc rupture" should be used. The term "annular gap" (referring to a relatively wide annular fissure) is non-standard ². 

Clinical presentation

Most are asymptomatic, however, some are painful. The defect allows ingrowth of nerve endings and granulation tissue. Fissures near the dorsal root ganglion are especially likely to be painful.

Pathology

Annular fissures may be radial, transverse or concentric in orientation. The fissure may involve all layers or only some. The distinction is difficult if no disc extrusion is seen.

Radiographic features

Fluoroscopy

Discography (introduction of contrast into the nucleus pulposus) can help distinguish partial thickness or full thickness annular fissure, although the clinical relevance of this is disputed. Tears are graded based on the modified Dallas classification which describes the extension of contrast from the nucleus pulposus through the annulus fibrosus.

MRI

Although very common, only a minority are identified on MRI.

Annular fissures are characterised by a region of high T2 signal (high intensity zone) in the otherwise low signal annulus ³. These can remain present for many years on follow up imaging.

Annular fissures are most commonly found in the lumbar spine but have also been described in the cervical spine ⁴.